Optical fibers find many uses for directing beams of light between two points. Optical fibers have been developed to have low loss, low dispersion, polarization maintaining properties and can also act as amplifiers. As a result, optical fiber systems find widespread use, for example in optical communication applications and remote sensing.
Wavelength, optical power and polarization are important properties of the light signals propagating in a fiber optic system. Components within the system may modify the propagation of the signals by changing one or more of these properties. For example, multiple signals may be transmitted through a single fiber optic by combining the outputs from a plurality of laser transmitters, each transmitter having an output wavelength that is restricted to a unique spectral band. Amplitude and/or frequency modulation may be used to encode information on the transmitter outputs. The polarization property may be used for network operations that include the tuning, multiplexing, demultiplexing and switching of light signals, for example.
Systems that utilize the polarization property of light often require light signals to be separated or combined according to their polarization state. A single fiber optic device may be designed to carry out both processes, separating signals from a combined input that propagates through the device in a first direction and combining polarized signals that propagate through the device in the opposite direction.
Polarization beam separator/combiners for use in fiber optic systems may use non-guiding optical components to separate/combine the optical signals as they propagate through the device along free-space optical paths. Collimating lenses are typically used to couple the light propagating along the free-space optical paths to the input/output waveguides with a one-to-one correspondence between lenses and waveguides. Thus a polarization separator/combiner with three input/output waveguides typically incorporates three lenses that must be accurately aligned with respect to the waveguides and the free-space optical paths.
Conventional polarization separator/combiners share several common disadvantages that derive from the one-to-one correspondence between fibers and focusing optical systems. For example, the low-loss propagation of light is facilitated by the accurate alignment of the optical focusing assemblies to the optical fibers. Alignment tolerances may be of the order of one micron and must be maintained against both temperature variations and vibration during the operational lifetime of the device. Typically, the optical components are housed in a mechanical alignment and support assembly that increases in complexity, size and cost with the number optical coupling components. It is, therefore, disadvantageous to use a dedicated optical focusing assembly to couple each of the optical fibers